1. Field of the Invention:
The present invention relates to the destruction, or consumption, of hypochlorites or ClO.sup.- ions present in a chlorate solution of an alkali metal, such as the solution of sodium chlorate resulting from the electrolysis of an aqueous solution of the chloride of said alkali metal, for example a solution of sodium chloride, prior to the crystallization of the chlorate values therefrom.
2. Description of the Prior Art:
Except for allowing the chlorate solution to remain in a so-called evolution reactor upon its withdrawal from the electrolysis cell for a period of time that is incompatible with the requirements of industrial production, it is known to this art that significant amounts of hypochlorite remain in such solution after evolution, to cause significant corrosion of the crystallizer, which typically is made of carbon or stainless steel.
It is also known to introduce additives into the chlorate solutions, such as, for example, sulfur dioxide, ammonia or urea.
However, sulfur dioxide requires careful handling, is harmful in nature, and results in the formation of sulfates, while at the same time the sulfates are being eliminated from the brines to be electrolyzed.
Ammonia in turn may form chloramines, which themselves are corrosive and which present the risk of explosion. This is also the case if urea is added, according to published European Application No. 0,266,129.
Thus, serious need continues to exist in this art for means other than mere passage of time or the above additives for destroying as completely as possible the hypochlorite values contained in a chlorate solution prior to the crystallization of the chlorate therefrom.
Although it is known that hydrogen peroxide reacts with ClO.sup.- ions, no process has to date been described for the destruction of such ions by means of H.sub.2 O.sub.2 introduced into an alkali metal chlorate solution emanating from the electrolysis of a chloride solution of said alkali metal in the presence of hexavalent chromium, typically in the form of a bichromate thereof, such as sodium bichromate Na.sub.2 Cr.sub.2 O.sub.7. The presence and conservation of the hexavalent chromium are necessary for the chromate process, as particularly described in the above '129 European application.
In such a case, the disappearance of hexavalent chromium would indeed be expected, for example if the chlorate solution is treated with a sulfur compound, such as water soluble sulfides according to FR 2,168,530.